A method for detecting and locating faults in oil-immersed transformers

Abstract

This application provides a method for fault detection and location in an oil-immersed transformer, comprising: identifying high-temperature regions in a dynamic temperature distribution, excluding uniformly heated regions formed by the background temperature of the top oil layer, extracting the upward trajectory of the high-temperature core formed by the extension of the initial layer, and delineating the vertical expansion boundary; acquiring the load history and cooling conditions during operation, reading the top and bottom oil temperatures, analyzing the heat energy distribution of the upper and lower oil layers during the continuous load phase, and identifying the oil temperature stratification morphology formed by natural oil circulation; using a hot oil plume transport model to analyze the plume channel and vertical expansion boundary, tracing the upward path of the hot oil along the initial layer, and identifying the internal search area defined by the axial section and the direction adjacent to the tank wall; acquiring the local oil temperature within the internal search area, identifying the internal oil layers and return interfaces that the hot oil passes through when it travels from the heat source to the tank wall, extracting the heat energy accumulation boundary along the plume channel, and forming a candidate fault source area.

Description

Technical Field

[0001] This invention relates to the field of information technology, and in particular to a method for fault detection and location of oil-immersed transformers. Background Technology

[0002] As a core component of the power system, the accurate location of internal faults in oil-immersed transformers directly impacts the safe operation of the power grid and the efficiency of equipment maintenance. Ideally, the location of internal faults could be accurately inferred by identifying abnormally high-temperature areas on the transformer tank wall surface using infrared imaging. However, in practical applications, it has been found that the natural circulation characteristics of transformer oil alter the heat transfer path, leading to a systematic deviation between the location of the high-temperature zone displayed on the tank wall surface and the actual fault source location. This deviation stems from the dynamic influence of heating intensity on the heat transfer path; when an internal overheating fault occurs, the heat transfer process is strongly interfered with by the buoyancy of the oil flow. To more easily identify internal faults, it is generally desirable for the fault point to have a large heating power to form a significant temperature anomaly zone on the tank wall. While increased heating power makes the high-temperature zone on the tank wall more prominent and easier to observe, the height of the temperature peak continuously shifts upwards, creating an expanded abnormal temperature distribution when superimposed on the background oil temperature at the top layer. This disrupts the spatial correspondence between surface features and the internal fault source. This is because when the heat output at the fault point increases, the buoyancy force generated by the localized rise in oil temperature strengthens. Driven by buoyancy, the hot oil accelerates upwards in the tank, transporting the fault heat over a large vertical area. Furthermore, this positional shift dynamically changes with parameters such as heat output and oil flow velocity. Increasing the salience of fault characteristics often reduces the accuracy of fault location. Therefore, under conditions where oil flow and thermal transport cause severe distortion of surface features, how to reverse-engineer the actual spatial location of internal faults through observable temperature evolution processes on the outside of the tank wall has become a pressing technical challenge. Summary of the Invention

[0003] This invention provides a method for fault detection and location in an oil-immersed transformer, the method comprising: Continuous infrared video of multiple outer surfaces of the fuel tank is acquired, and the continuous images are organized according to the coverage of each side of the tank wall. The continuous outline of the heating area in the front and back images is identified to form a dynamic temperature distribution that reflects the heating process of the tank wall. Identify high-temperature regions in dynamic temperature distribution, exclude uniformly heated regions formed by the top oil temperature background, extract the upward trajectory of the high-temperature core formed by the extension of the initial layer, and delineate the vertical expansion boundary. Acquire the load history and cooling conditions during operation, read the top oil temperature and bottom oil temperature, analyze the heat energy distribution of the upper and lower oil layers, and identify the oil temperature stratification morphology formed by natural oil circulation. Analyze the upward trajectory of the high-temperature core and the oil temperature stratification morphology, identify the heating profile that stays in the local area of ​​the tank wall and the extended profile that rises with the oil layer, distinguish between local heating in the tank wall and heating carried by the oil flow, and form a plume channel for fault thermal energy. A hot oil plume transport model was used to analyze the plume channel and vertical expansion boundary, and the hot oil rising path was traced along the initial emergence layer to identify the internal search area defined by the axial section and the direction of the adjacent box wall. The local oil temperature within the internal search area is obtained, the internal oil layer and reflux interface that the hot oil passes through when it flows from the heat source to the tank wall are identified, and the heat energy accumulation boundary is extracted along the plume channel to form a candidate area for the fault source. Identify the heat source by traversing the hot oil passage within the candidate fault source area, analyze the coverage direction of the accumulation boundary on multiple side walls, assess the fault range extending along the adjacent wall within the axial section, and pinpoint the internal overheating fault area.

[0004] Preferably, the step of acquiring continuous infrared video of multiple outer surfaces of the fuel tank, organizing the continuous images according to the coverage area of ​​each side of the tank wall, identifying the continuous outline of the heating area in the preceding and following images, and forming a dynamic temperature distribution reflecting the heating process of the tank wall includes: Infrared cameras are deployed on the outside of the four side walls to acquire continuous infrared video. The continuous images are spliced ​​and time-aligned according to the coverage of each side wall to obtain a sequence of infrared images for each side. Inter-frame contour matching is used to track the position of the heating zone in adjacent images. The boundary of the same heating zone is connected to obtain a continuous contour and superimposed along the time axis to obtain a dynamic temperature distribution.

[0005] Preferably, the process of identifying high-temperature regions in the dynamic temperature distribution, excluding uniformly heated regions formed by the top-layer oil temperature background, extracting the upward trajectory of the high-temperature core formed by the extension of the initial layer, and delineating the vertical expansion boundary includes: The connected regions whose temperatures exceed a preset temperature threshold are extracted from the dynamic temperature distribution as high-temperature zones. The top oil temperature background with a horizontal temperature difference less than a preset amplitude at the top of the tank wall is removed. The vertical height of the earliest appearing connected region with an outline area exceeding a preset minimum area is taken as the initial appearance layer. The centroid of the candidate high-temperature zones is obtained by tracking the centroids frame by frame to obtain the upward trajectory of the high-temperature core. The position of the tank wall where the horizontal temperature gradient decays to a preset gradient threshold is taken as the outer edge of the vertical expansion boundary.

[0006] Preferably, the step of reading the top oil temperature and bottom oil temperature, analyzing the thermal energy distribution of the upper and lower oil layers, and identifying the oil temperature stratification morphology formed by natural oil circulation includes: The top oil temperature is read from the temperature measuring point at the top of the chamber, and the bottom oil temperature is read from the temperature measuring point at the bottom of the chamber. The oil temperature distribution is obtained by linear interpolation along the height of the chamber according to the thermal buoyancy stratification law, with the top oil temperature and the bottom oil temperature as the two vertical endpoints. The oil temperature distribution with the calibrated temperature increasing monotonically from bottom to top and the temperature difference between the top and bottom being within the preset temperature difference range is the oil temperature stratification form.

[0007] Preferably, the analysis of the high-temperature core's upward trajectory and oil temperature stratification morphology, identifying the heating profile localized on the tank wall and the extended profile rising with the oil layer, distinguishing between localized heating on the tank wall and heating carried by the oil flow, and forming a plume channel for fault thermal energy, includes: The vertical height of each sampling point on the high-temperature core rising trajectory is substituted into the oil temperature stratification pattern. The oil temperature at the same vertical height is taken as the stratification oil temperature reference value. The abnormal trajectory segment sequence with the sampling point temperature exceeding the stratification oil temperature reference value is calibrated. The displacement segments between adjacent sampling points of the abnormal trajectory segment sequence are classified, and the displacement segments attached to the inner surface of the tank wall are determined to be heating profiles that remain in the local area of ​​the tank wall, and the displacement segments that extend upward along the high oil temperature layer are extended profiles that float with the oil layer. The heating profile that remains on the local wall of the tank and the extended profile that rises with the oil layer are connected in series and the intersection of the two are marked. The plume channel of the fault thermal energy is obtained by collecting the intersections.

[0008] Preferably, the step of identifying the heating profile localized on the tank wall and the extended profile rising with the oil layer, distinguishing between localized heating on the tank wall and heating carried by the oil flow, and forming a plume channel for fault thermal energy includes: The vertical height of the sampling point where the first abnormal temperature rise occurs on the high-temperature core's upward trajectory is taken as the initial occurrence layer. The contour displacement segment between the initial occurrence layer and the vertical expansion boundary is intercepted along the high-temperature core's upward trajectory. This segment is then included in the continuous overlapping segments attached to the box wall at the same vertical height and with a regional overlap rate exceeding a preset overlap threshold. This segment is also included in the upward migration segment across adjacent vertical layers. The continuous overlapping segments attached to the box wall and the upward migration segment across the oil layer are connected in series, and the intersection position is marked to obtain the plume channel.

[0009] Preferably, the step of using a hot oil plume transport model to analyze the plume channel and vertical expansion boundary, and tracing the upward path of the hot oil along the initial emergence layer, includes: The hot oil plume transport model adopts an axisymmetric turbulent buoyancy plume model. The plume rise path is obtained by using the intersection position coordinates and the vertical displacement of the upward segment across the oil layer as the fitting input and the horizontal offset of the corresponding height relative to the box wall as the fitting output. The plume rise path is tracked along the initial appearance layer and mapped into the box to obtain candidate axes. The part of the winding column corresponding to the candidate axis within the height limited by the vertical extension boundary is calibrated as the axial segment. The three-dimensional space enclosed by the axial segment along the vertical direction and the adjacent box wall along the horizontal direction is taken as the internal search area.

[0010] Preferably, obtaining the local oil temperature within the internal search area includes: The local oil temperatures are arranged into a two-dimensional oil temperature field according to spatial coordinates. The continuous section with a monotonically increasing vertical temperature and a temperature difference between adjacent measuring points greater than a preset increasing threshold is defined as the internal oil layer. The transition zone where the oil temperature suddenly drops to a level less than a preset threshold and the difference between the oil temperature and the bottom layer oil temperature is defined as the reflux interface. The arithmetic mean of the oil temperatures at the top of the internal oil layer and the bottom of the reflux interface is taken as the boundary oil temperature. The set of connected pixels with local oil temperatures higher than the boundary oil temperature is defined as the thermal energy accumulation boundary to obtain the candidate fault source region.

[0011] Preferably, the step of identifying the heat source along the hot oil passage within the candidate fault source area and analyzing the coverage direction of the accumulation boundary on the multi-sided tank wall includes: The main heating path is formed by connecting continuous measuring points with monotonically increasing local oil temperature along the plume channel. The continuous high-temperature measuring point string from the bottom of the main heating path to the bottom is calibrated as the hot oil passage channel. The weighted geometric center of the high-temperature pixel set at the bottom of the hot oil passage channel is taken as the heat source. The side of the box wall to which the shortest vertical distance between the calibrated heat energy accumulation boundary and the inner surface of the box wall is less than the preset wall-attaching distance threshold is the covering side, and the normal of the inner surface of the covering side is taken as the covering direction. Extending horizontally along each coverage direction from the heat source within the vertical height limited by the axial section, the horizontal span of the set of connected pixels where the local oil temperature is higher than the boundary oil temperature is taken as the fault range, and the three-dimensional space enclosed by the fault range and the axial section is defined as the internal overheating fault area.

[0012] Preferably, the continuous high-temperature measuring point string tracing from the lower end of the main heating path to the lowest end is calibrated as a hot oil passage channel, and the weighted geometric center of the high-temperature pixel set at the bottom of the hot oil passage channel is taken as the heat source, including: Take a horizontal cross-section at the initial layer height of each hot oil passage, and take the closed contour enclosed by the heat energy accumulation boundary as the horizontal cross-section heat energy boundary. Take the arc line that coincides with the contact of the inner oil layer and the inner surface of the adjacent tank wall as the contact arc segment. Mark the equidistant midpoints of the contact arc segment as the intersection of the hot oil passage from the inner oil layer to the adjacent tank wall. Connect the intersections in the same axial section according to the coverage direction to obtain the fault range extending along the tank wall direction.

[0013] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects: This invention discloses a method for fault detection and location in oil-immersed transformers. Addressing the challenge of distinguishing between localized heating and oil-borne heat during transformer tank wall heating, it integrates continuous infrared video, oil temperature stratification analysis, and a hot oil plume transport model into a complete technology chain. First, the invention organizes continuous images according to the coverage area of ​​each tank wall, identifies the continuous contour of the heating area, and eliminates uneven areas caused by the top oil temperature background, extracting the upward trajectory of the high-temperature core. Then, combining load history and upper and lower oil temperature distribution, it identifies the oil temperature stratification pattern, distinguishing between the local contour remaining on the tank wall and the extended contour rising with the oil layer. It marks the intersection positions of continuous overlapping sections attached to the tank wall and sections moving upward across oil layers, converging them into a plume channel. Finally, the hot oil plume transport model tracks the upward path of the hot oil along the initial stratum and delineates the internal search area, extracting the heat energy accumulation boundary to lock the candidate fault source area. Connecting the intersection positions on multiple tank walls in the same axial section, it completes the precise location of internal overheating faults, significantly improving fault detection sensitivity and location accuracy. Attached Figure Description

[0014] Figure 1 This is a flowchart of a method for fault detection and location of an oil-immersed transformer according to the present invention.

[0015] Figure 2 This is a schematic diagram of a fault detection and location method for an oil-immersed transformer according to the present invention.

[0016] Figure 3 This is another schematic diagram of a fault detection and location method for an oil-immersed transformer according to the present invention. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and thoroughly described below with reference to the accompanying drawings. The described embodiments are merely some embodiments of the present invention.

[0018] like Figures 1-3 This embodiment of a method for fault detection and location in an oil-immersed transformer may specifically include: Step S101: Acquire continuous infrared video of multiple outer surfaces of the oil tank, organize the continuous images according to the coverage of each side of the tank wall, identify the continuous outline of the heating area in the front and back images, and form a dynamic temperature distribution that reflects the heating process of the tank wall.

[0019] Infrared cameras are deployed on the exterior of the four side walls of the oil-immersed transformer to acquire continuous infrared video of the multiple outer surfaces of the tank. The continuous images are stitched together and time-aligned according to the coverage area of ​​each side wall to obtain a sequence of infrared images covering the entire surface of the tank wall. In this sequence, heated areas with temperatures higher than the surrounding areas are identified. Inter-frame contour matching is used to track the positional continuity of these heated areas in adjacent images. The boundaries of the same heated area in consecutive images are concatenated to obtain a continuous contour. This continuous contour is then superimposed along the time axis onto the coverage area of ​​each side wall to obtain a dynamic temperature distribution reflecting the heating process of the tank wall.

[0020] In the infrared monitoring scenario of oil-immersed transformers, the temperature evolution of the outer surface of the transformer tank wall carries important information about the internal heat source.

[0021] For example, an uncooled infrared thermal imager is installed on each of the four sides of the transformer tank wall, directly opposite to it. The recording range covers the high, middle, and low layers of the tank wall, with a sampling frequency of 1 to 5 frames per second. The optical axis of the recording device is aligned with the normal of the tank wall to avoid directional attenuation of surface emissivity and geometric projection distortion caused by oblique viewing angles. The infrared recording devices are started synchronously to obtain continuous infrared video of the multiple outer surfaces of the tank.

[0022] Specifically, in acquiring the side-mounted infrared image sequence, continuous images are categorized by side according to the physical boundaries of each side of the enclosure wall. Adjacent images on the same side are time-aligned according to their recording timestamps, resulting in a side-mounted infrared image sequence covering the entire surface of that side of the enclosure wall. In one embodiment, the corner area of ​​the enclosure wall is simultaneously covered by cameras on both sides. Considering the attenuation caused by the oblique viewing angle on both sides of the corner, the side with the higher radiation temperature in the two images is taken as the representative value for that area to compensate for the temperature underestimation caused by the oblique viewing angle, thus obtaining the compensated radiation temperature value for the corner. When identifying the heating zone in the side-mounted infrared image sequence, the radiation temperature of each pixel in the image is compared with the average background temperature of its neighboring area. Pixels exceeding a preset temperature difference threshold are connected to form a region, which is then designated as the heating zone.

[0023] Preferably, the natural temperature difference fluctuation range is obtained by taking frame-by-frame temperature samples of the chamber wall surface during 7 consecutive days of fault-free operation. The absolute value sequence of temperature difference between frames is statistically analyzed at 5-minute recording intervals. The standard deviation σ of this sequence represents the fluctuation amplitude. The preset temperature difference threshold is set to 2σ to 3σ, with typical samples falling between 2 and 5 degrees Celsius, avoiding the misclassification of false heating zones caused by environmental temperature disturbances and natural temperature differences of the chamber wall. For the continuity of the same heating zone in adjacent frames, inter-frame contour matching is used for tracking: using the boundary of the heating zone in the previous frame as a reference, a candidate region with the closest centroid distance and an area overlap exceeding a preset ratio is searched in the subsequent frame, with the two regions being continuous. The preset ratio is determined by adding a margin to the statistical lower bound of the overlap of adjacent frames with the same continuous contour in the 7 consecutive days of fault-free operation samples, and is set to 0.6 to 0.8. Thus, the boundaries of the same heating zone in the preceding and following frames are concatenated to obtain the continuous contour. The continuous contour is superimposed frame by frame along the time axis onto the coverage area of ​​each side box wall to form a three-dimensional temperature sequence with the horizontal position and vertical height on the unfolded surface of the box wall as two spatial coordinates and the recording time as the time dimension, thus obtaining a dynamic temperature distribution that reflects the heating process of the box wall.

[0024] It is understandable that the dynamic temperature distribution preserves the occurrence layer, expansion direction, and temperature peak change process of the heating zone over time, providing basic data for subsequent interpretation of the high-temperature core and oil temperature stratification morphology.

[0025] Step S102: Identify the high-temperature region in the dynamic temperature distribution, exclude the uniform heating region formed by the top oil temperature background, extract the high-temperature core rising trajectory formed by the extension of the initial layer, and delineate the vertical expansion boundary.

[0026] From the dynamic temperature distribution, connected regions with temperatures exceeding a preset temperature threshold are extracted as high-temperature zones. The horizontal temperature difference amplitude within the top region of the tank wall is read, and connected regions with temperature difference amplitudes less than a preset amplitude are marked as top-layer oil temperature backgrounds and removed from the high-temperature zones, resulting in candidate high-temperature zones after removing the top-layer background. Within these candidate high-temperature zones, the vertical height of the tank wall where the earliest appearing connected region with an outline area exceeding a preset minimum area is located is taken as the initial appearance layer. The centroid positions of the candidate high-temperature zones in subsequent frames are concatenated using frame-by-frame centroid tracking to obtain the upward trajectory of the high-temperature core extending from the initial appearance layer. Along both sides of the upward trajectory of the high-temperature core, the horizontal temperature gradient of the candidate high-temperature zone outline relative to the trajectory centerline in adjacent frames is read. The tank wall position where the horizontal temperature gradient decays to a preset gradient threshold is taken as the outer edge of the vertical expansion boundary. The outer edges in each frame are concatenated to obtain the upward trajectory of the high-temperature core and its vertical expansion boundary.

[0027] During the temperature evolution of the tank wall of an oil-immersed transformer, the dynamic temperature distribution simultaneously carries the high-temperature core caused by the internal fault heat source and the background temperature rise formed by the stratification of the top oil temperature. Both are represented in infrared images as connected areas with temperatures higher than the surrounding areas.

[0028] For example, the high-temperature core caused by the fault heat source usually appears at a certain vertical height on the tank wall in the early stage of the fault and floats upwards vertically over time; while the top oil temperature background rises uniformly over a large area in the horizontal direction on the upper part of the tank wall. Distinguishing between the two is a prerequisite for accurately locating the upward trajectory of the high-temperature core.

[0029] Specifically, from each frame of the dynamic temperature distribution, connected regions with temperatures exceeding a preset temperature threshold are extracted as high-temperature zones. The preset temperature threshold is determined by adding a certain margin to the average background temperature of the tank wall during fault-free operation, typically 5 to 8 degrees Celsius above the average background temperature. The images of each of the four sides of the tank wall are processed separately to obtain a set of high-temperature zones covering each side of the tank wall. In one embodiment, the process of stripping the top layer oil temperature background is as follows: The radiation temperature values ​​of each pixel on the same horizontal line are read from an area covering approximately 1 / 5 to 1 / 4 of the total height of the tank wall. The difference between the maximum and minimum values ​​of the radiation temperature values ​​is calculated as the horizontal temperature difference amplitude. If the horizontal temperature difference amplitude is less than the preset amplitude, the connected region where the horizontal line is located is determined to be a uniformly heated area caused by the top layer oil temperature background and is removed from the high-temperature zone set. The preset amplitude is typically 1 to 2 degrees Celsius, used to distinguish the approximately uniformly distributed top layer oil temperature rise along the horizontal direction of the tank wall from locally concentrated fault heat sources. The remaining connected regions after stripping the top layer background constitute candidate high-temperature zones.

[0030] It should be noted that the candidate high-temperature zones exhibit a dynamic migration characteristic from low to high over time, reflecting the upward movement of hot oil emitted by the faulty heat source under buoyancy. Among the candidate high-temperature zones, the earliest appearing frame is taken as the reference frame. Connected regions in the reference frame whose outline area exceeds a preset minimum area are read, and the vertical height of the center point of this connected region on the unfolded surface of the tank wall is marked as the initial appearance layer. The preset minimum area is determined according to the pixel scale of the infrared thermal imager, generally ranging from 30 to 80 pixels. High-temperature zones below the initial appearance layer are not accepted to prevent accidental hot spots caused by reflections from the tank wall itself or environmental heat sources from being mistakenly included. Furthermore, a frame-by-frame centroid tracking method is used to connect the centroid positions of the candidate high-temperature zones in subsequent images: using the centroid position of the previous frame as the center, candidate high-temperature zones with a centroid distance less than a preset displacement threshold are searched in the next frame and determined to be continuations of the same high-temperature core. The centroids of the two frames are connected with a straight line segment; the centroids of each adjacent frame are sequentially connected along the recording time axis to obtain the upward trajectory of the high-temperature core extending from the initial appearance layer. The preset displacement threshold is determined by the product of the natural rising speed of hot oil and the recording sampling interval.

[0031] In one possible implementation, the vertical expansion boundary refers to the vertical envelope of the heated area of ​​the box wall affected by the lateral conduction of heat to both sides of the box wall during the upward migration of the high-temperature core from its initial appearance layer. This boundary is used to define the termination position of the subsequent displacement segment. The determination process is as follows: For each frame containing the candidate high-temperature area of ​​the high-temperature core, the vertical line where the centroid is located is taken as the trajectory centerline. The radiation temperature value is read outward pixel by pixel along the horizontal direction. The temperature difference between adjacent pixels is calculated as the lateral temperature gradient G, i.e., G = Ti + 1 - Ti, where Ti is the radiation temperature at the i-th pixel from the centerline. Starting from the trajectory centerline, the frame wall position where G first decays to the preset gradient threshold Gth is taken as the outer edge point of the frame. Gth is selected based on the thermal conductivity of the box wall material and the magnitude of the background temperature fluctuation. Generally, it is taken as 0.2 degrees Celsius per pixel to 0.5 degrees Celsius per pixel. When the box wall is thin or the environmental interference is small, the lower limit is taken, and vice versa. In this embodiment, it is taken as 0.3 degrees Celsius per pixel. The left and right outer edge points in each frame are sequentially connected according to the recording timestamp and then smoothed by three-point sliding to form two outer edge curves located on both sides of the upward trajectory of the high-temperature core. The box wall area covered by the two outer edge curves in the vertical direction is the vertical expansion boundary, and its upper endpoint is the end point of the upward displacement segment.

[0032] It is understood that the upward trajectory of the high-temperature core reflects the apparent upward path of the hot oil emitted by the faulty heat source outside the tank wall. Samples are taken at intervals of 0.05 meters along the height of the tank wall, and recorded as a set of longitudinal coordinate sequences z1 to zn. The vertical expansion boundary follows the vertical expansion boundary determined by the two outer edge curves determined by the lateral temperature gradient decay. The horizontal width w corresponding to any height z is the distance between the two outer edge curves on the left and right at that height. The sampling times of z1 to zn and each sampling point serve as the basis for querying the reference value of the stratified oil temperature at the same height and for extracting the vertical coordinates of abnormal trajectory segments. The horizontal width w corresponding to any height z is output along with the vertical expansion boundary to characterize the lateral spread range of the high-temperature core.

[0033] Step S103: Obtain the load history and cooling conditions during operation, read the top oil temperature and bottom oil temperature, analyze the heat energy distribution of the upper and lower oil layers during the continuous load phase, and identify the oil temperature stratification morphology formed by natural oil circulation.

[0034] The load history and cooling conditions during the operation of the oil-immersed transformer are obtained. The top oil temperature is read from the temperature measuring point at the top of the tank, and the bottom oil temperature is read from the temperature measuring point at the bottom of the tank. The load history and cooling conditions are aligned on the same time axis, and the period when the load remains at a stable level is selected as the load duration phase. Within the load duration phase, the top and bottom oil temperatures are used as the vertical endpoints, and linear interpolation is performed along the tank height according to the stratification law driven by thermal buoyancy to obtain the oil temperature distribution that changes continuously along the vertical direction. The oil temperature distribution is judged to have a monotonically increasing temperature from bottom to top, and the temperature difference between the top and bottom layers is stable within a preset temperature difference range. The oil temperature distribution that conforms to the above pattern is determined to be an oil temperature stratification pattern formed by natural oil circulation.

[0035] In the operation monitoring scenario of oil-immersed transformers, the load history during operation is retrieved from the transformer's monitoring terminal. The load history includes the value sequence of high-voltage side current, low-voltage side current, and active power over time. Simultaneously, the cooling conditions recorded by the monitoring terminal are retrieved, including the cooler switching status, cooling fan speed, and inlet and outlet temperatures of the cooling medium.

[0036] For example, the sampling time interval is 1 to 5 minutes, covering the entire observation period.

[0037] Specifically, a platinum resistance thermometer is installed at the top of the transformer tank near the oil conservator to read the top oil temperature; another platinum resistance thermometer is installed at the bottom of the transformer tank near the bottom valve to read the bottom oil temperature. After aligning the load history, cooling conditions, top oil temperature, and bottom oil temperature along the same time axis, the active power is used as the load metric, and its percentage relative to the transformer's rated capacity is taken as the load level. The period during which the load level remains stable within a preset fluctuation range is identified as the load duration phase. In one embodiment, the preset fluctuation range is ±5% of the rated capacity, and the cooling conditions are maintained at the same level for at least 30 minutes to be included in the load duration phase. Within the load duration phase, using the height of the top temperature measuring point (where the top oil temperature is located) as the vertical upper endpoint and the height of the bottom temperature measuring point (where the bottom oil temperature is located) as the vertical lower endpoint, linear interpolation is performed according to a layered pattern that increases approximately linearly from bottom to top along the tank height under thermal buoyancy drive, resulting in a continuously varying oil temperature distribution along the vertical direction. The oil temperature distribution reflects the thermal energy distribution of the upper and lower oil layers during the continuous load phase.

[0038] Understandably, in natural oil circulation, heat is generated at the bottom of the windings, rises with the oil flow to the upper part of the tank, and then flows back through the cooler. The oil temperature inside the tank exhibits a steady-state gradient that monotonically increases from bottom to top. The oil temperature distribution is characterized by a monotonically increasing temperature from bottom to top, with the temperature difference between the top and bottom layers remaining stable within a preset temperature difference range. This preset temperature difference range is determined based on the statistical range of the temperature difference between the top and bottom layers under steady-state natural oil circulation of the same type of transformer, ranging from 10 degrees Celsius to 25 degrees Celsius. Oil temperature distributions conforming to this pattern are considered to be oil temperature stratification patterns formed by natural oil circulation.

[0039] Step S104: Analyze the upward trajectory of the high-temperature core and the oil temperature stratification morphology, identify the heating profile that stays in the local area of ​​the tank wall and the extended profile that rises with the oil layer, distinguish between local heating of the tank wall and heating carried by the oil flow, and form a plume channel for fault thermal energy.

[0040] The high-temperature core's upward trajectory and oil temperature stratification pattern are obtained. The vertical height of each sampling point on the high-temperature core's upward trajectory is substituted into the oil temperature stratification pattern. The oil temperature at the same vertical height is taken as the stratified oil temperature reference value for that sampling point. The temperature of the sampling point on the high-temperature core's upward trajectory is subtracted from the stratified oil temperature reference value. The sampling point segments with a temperature difference exceeding a preset temperature difference threshold of 3 degrees Celsius are calibrated to obtain an abnormal trajectory segment sequence carrying fault thermal information. The displacement segments between adjacent sampling points in the abnormal trajectory segment sequence are classified. If the vertical displacement of the displacement segment is less than a preset dwell displacement threshold of 0.03 meters and its lateral coordinate is less than a preset attachment distance of 0.02 meters, it is determined to be a localized heating profile dwelling on the tank wall. If the vertical displacement of the displacement segment is greater than a preset upward displacement threshold of 0.1 meters and extends upward along the high oil temperature layer of the oil temperature stratification pattern, it is determined to be an extended profile rising with the oil layer, thus distinguishing between localized heating on the tank wall and heating carried by the oil flow. The heating profile that remains on the local wall of the tank and the extension profile that rises with the oil layer are sequentially connected in time along the abnormal trajectory segment sequence. The intersection position of the two is marked, and each intersection position and its corresponding extension profile that rises with the oil layer are collected to obtain the plume channel of the fault thermal energy.

[0041] The high-temperature core rising trajectory observed outside the tank wall of an oil-immersed transformer carries information about the heat generated by the fault source, and also includes background temperature rise contributed by the oil temperature stratification formed by natural oil circulation. To separate the two, each point of the trajectory needs to be placed back into the stratified oil temperature background corresponding to its vertical height for comparison.

[0042] In one possible implementation, each sampling point on the upward trajectory of the high-temperature core is taken, and its vertical height is used as the query key to enter the oil temperature distribution that changes continuously along the vertical direction as described by the oil temperature stratification pattern to query the oil temperature reading at the same height. This reading is used as the stratified oil temperature reference value of the sampling point to obtain a sequence of stratified oil temperature reference values ​​corresponding to each point on the upward trajectory of the high-temperature core.

[0043] Specifically, the wall heat transfer correction ΔTb(h) at each vertical height is first calibrated according to the fault-free steady-state period: the sliding average of the difference between the wall radiation temperature and the reference value of the stratified oil temperature at the same height during the fault-free steady-state period is taken as ΔTb(h) and stored; the radiation temperature of each sampling point on the high-temperature core rising trajectory is corrected by adding ΔTb(h) of its height to the equivalent oil temperature, and then the equivalent oil temperature is subtracted from the reference value of the stratified oil temperature to obtain the temperature difference value of the sampling point relative to the stratified background.

[0044] For example, if the temperature difference exceeds a preset temperature difference threshold, the sampling point is determined to carry additional thermal information contributed by the fault source and is marked as an abnormal sampling point. The preset temperature difference threshold is determined by three times the sum of the fitting residual of the layered oil temperature reference value and the infrared temperature measurement error, and is set to 3 degrees Celsius.

[0045] It should be noted that the normal distances d1 and d2 from the sampling points at both ends to the inner surface of the transformer tank wall as reflected in the infrared image on that side are simultaneously read as the adhesion measurement. If |dy| is less than the preset dwell displacement threshold of 0.03 meters, and both d1 and d2 are less than the preset adhesion distance threshold of 0.02 meters, then the displacement segment is determined to be a localized heating profile on the tank wall and is classified as localized heating on the tank wall. Instead, the ratio of the intersection area to the union area of ​​the high-temperature profile projection areas of adjacent images is calculated simultaneously according to the caliber in S1041 as the region overlap rate. If |dy| is not greater than the preset dwell displacement threshold of 0.03 meters, and the region overlap rate is greater than the preset overlap threshold of 0.7, then the displacement segment is determined to be a localized heating profile on the tank wall and is classified as localized heating on the tank wall. In one embodiment, the infrared images on each side are simultaneously acquired by infrared thermal imagers arranged on the front, back, left, and right sides of the transformer tank, one on each side, with the optical axis roughly perpendicularly aligned with the middle of the tank wall on that side, and the acquisition frame rate is aligned with the timing of the trajectory sampling points. The side wall of the enclosure is discretized into rectangular unfolded surfaces along its outer contour using an equidistant grid. The horizontal reference is the horizontal centerline of the enclosure wall, with leftward deviations being negative and rightward deviations positive. The vertical reference is the bottom of the enclosure, with upward deviations positive. For each abnormal sampling point, its pixel coordinates are first read from the infrared image of that side. Then, based on the intrinsic and extrinsic parameters of the thermal imager, the intersection of the pixel ray and the plane containing the side wall is determined using a pinhole imaging model. The position of the intersection point on the unfolded surface is the horizontal coordinate (x) and vertical coordinate (y) of the sampling point. The vertical coordinates of the sampling points at both ends of the displacement segment are denoted as y1 and y2. dy = y2 - y1 is taken as the vertical displacement, with upward deviations positive. Simultaneously, the normal distances d1 and d2 from the sampling points at both ends to the inner surface of the enclosure wall, as reflected in the infrared image of that side, are read as adhesion measurements. If |dy| is less than the preset dwell displacement threshold of 0.03 meters, and both d1 and d2 are less than the preset adhesion distance threshold of 0.02 meters, then the displacement segment is determined to be a localized heating profile within the enclosure wall, and it is classified as localized heating within the enclosure wall.

[0046] Specifically, the heating profile that stays on the local wall of the box reflects the component of the heat source being close to the box wall and mainly conducted outward through the metal body of the box wall itself. On the time axis, it is shown as an attachment form with the outline shape basically unchanged and the geometric center swinging slightly within the same vertical height band.

[0047] In one embodiment, a heating profile that remains on the local wall of the tank is considered valid only if it lasts for at least 5 sampling cycles, thus eliminating short-term adhesion caused by instantaneous interference. Another type of displacement segment differs from the aforementioned adhesion pattern: if the vertical displacement of a certain displacement segment is greater than a preset upward displacement threshold of 0.1 meters, the line connecting its two sampling points is vertically upward, and the initial and final sampling points belong to different vertical stratification zones defined by thresholds increasing by 1 degree Celsius, the stratified oil temperature reference value of the final zone is higher than that of the initial zone, and the connecting path crosses at least one stratification zone interface (i.e., both ends cross the high-temperature layer in the oil temperature stratification pattern), then the displacement segment is determined to be an extended profile that rises with the oil layer and is classified as heat carried by the oil flow. The determination is based solely on the defined vertical stratification zone, and no separate endpoint temperature difference threshold is set. If the number of layers crossed is two or more, it is considered to cross a more significant stratification gradient and is still classified into the same type of extended profile. The extended profile that rises with the oil layer reflects the composition of hot oil being transported upwards from the inside along the oil layer under the drive of buoyancy, and carrying the fault heat energy to a higher height of the tank wall during the ascent.

[0048] In one possible implementation, the heating profile that remains locally on the tank wall and the extension profile that rises with the oil layer alternate sequentially along the time axis, exhibiting an alternating pattern of attachment and upward movement from the initial appearance layer, with a clear morphological switching point between the two types of profiles. Further, along the time sequence of the abnormal trajectory segments, the heating profile that remains locally on the tank wall and the extension profile that rises with the oil layer are sequentially connected. At each position where the morphology changes from attachment to upward movement or from upward movement to attachment, the arithmetic mean of the horizontal and vertical coordinates of the sampling point before and after the switch on the unfolded surface of the tank wall is taken as the two-dimensional midpoint coordinates, and this two-dimensional midpoint coordinate is marked as the intersection position. Based on chronological order, the heating profile that remains locally on the tank wall is designated as the attachment segment, and the extended profile that rises with the oil layer is designated as the rising segment. The junction position is used as the common endpoint between adjacent segments. The end sampling point of the attachment segment is connected to the next junction position with a straight line segment, and then the junction position is connected to the beginning sampling point of the adjacent rising segment. The rising segment and the next attachment segment also transition through the junction position in the same way. Thus, all attachment segments, rising segments, and junction positions are connected end to end in chronological order to form a continuous broken line. The order between segments is arranged alternately between attachment and rising through the junction position according to the actual judgment results. The resulting broken line is the plume channel of the fault thermal energy. The attachment segment depicts the direction in which the thermal energy is briefly intercepted by the tank wall and accumulates locally along the wall surface. The rising segment depicts the direction in which the thermal energy is transported upward layer by layer with the oil flow. The junction position depicts the turning point and connection between the two directions, which together constitute the complete migration path of the fault thermal energy from the initial layer.

[0049] It is understandable that the plume channel separates and reassembles the localized heating of the box wall and the heating carried by the oil flow in time and space, stripping away the positional offset component caused by the oil flow transport, and providing a channel-level spatial reference for subsequently locking the internal search area along the axial section and the direction of the adjacent box wall.

[0050] Identify the initial layer in the high-temperature core's upward trajectory and oil temperature stratification morphology. Extract the contour displacement segments of each adjacent image between the initial layer and the vertical expansion boundary. Connect and mark the junction positions of the continuous overlapping segments attached to the box wall and the upward segments across the oil layer, and collect the junction positions and corresponding upward segments to form a plume channel.

[0051] The trajectory of the high-temperature core and the oil temperature stratification pattern are obtained. The vertical height of the sampling point where the first abnormal temperature rise occurs is taken on the trajectory of the high-temperature core. The stratification oil temperature reference value corresponding to this vertical height is queried in the oil temperature stratification pattern. The lowest vertical height corresponding to the sampling point where the radiation temperature exceeds the stratification oil temperature reference value by a preset temperature difference threshold of 3 degrees Celsius is determined as the initial occurrence layer. A sampling point segment is extracted from the initial occurrence layer upwards along the trajectory of the high-temperature core to the vertical expansion boundary, obtaining the contour displacement segment between adjacent images within this segment. For each contour displacement segment, its shape is determined. If the contours in adjacent images are attached to the box wall at the same vertical height and the regional overlap rate exceeds a preset overlap threshold of 0.7, it is classified as a continuous overlapping segment attached to the box wall. If the contours in adjacent images migrate upwards along the vertical direction across the adjacent vertical layer corresponding to the temperature increase reaching a preset increase threshold of 1 degree Celsius in the oil temperature stratification pattern, it is classified as an upward migration segment across oil layers. The continuous overlapping segments attached to the box wall and the upward-moving segments across the oil layer are connected in chronological order. Each position where the continuous overlapping segment attached to the box wall transitions to the upward-moving segment across the oil layer is marked as the junction position. The junction positions and their adjacent upward-moving segments across the oil layer are collected to obtain the plume channel of the fault thermal energy.

[0052] During the process of the heat generated by the fault source being carried upward by the oil flow, the height at which the heat energy can first be perceived by the infrared image on the box wall is often closest to the vertical position of the internal fault source. This height is the initial appearance layer and is the starting point of the subsequent plume channel.

[0053] Specifically, along the upward trajectory of the high-temperature core, each sampling point is traversed in chronological order, and its vertical height is used as the query key to enter the oil temperature distribution that continuously changes vertically as described by the oil temperature stratification pattern, and obtain the stratified oil temperature reference value at that vertical height. The radiation temperature of the sampling point is corrected by adding the wall heat transfer correction amount ΔTb(h) at its height to obtain the equivalent oil temperature, and then subtracted from the stratified oil temperature reference value to obtain the temperature difference value of the sampling point relative to the stratification background. ΔTb(h) is obtained according to the calibration method. In one embodiment, along the upward trajectory of the high-temperature core, each sampling point is traversed in chronological order. The vertical height corresponding to the earliest sampling point in the sampling point segment where the temperature difference value first exceeds a preset temperature difference threshold of 3 degrees Celsius for three consecutive sampling cycles is calibrated as the initial occurrence layer of the upward trajectory of the high-temperature core. This serves as a verification and correction of the initial occurrence layer. If the verification result is inconsistent with the calibration result, the verification result shall prevail to avoid false initial determination caused by instantaneous interference of a single sampling point. Starting from the initial appearance layer, sampling points are sequentially extracted upwards along the upward trajectory of the high-temperature core until the upper boundary defined by the vertical expansion boundary is reached. The line connecting the corresponding sampling points between every two adjacent frames within the extracted interval is taken as the contour displacement segment, resulting in a sequence of contour displacement segments reflecting the frame-by-frame displacement of the high-temperature core.

[0054] It should be noted that the contour displacement segments are divided into two categories according to their movement patterns: one category is the displacement segment in which the contour position and shape of the high-temperature core in adjacent frames do not change much and always sticks to the same section of the box wall; the other category is the displacement segment in which the contour of the high-temperature core in adjacent frames clearly migrates upwards along the vertical direction across different temperature zones in the oil temperature stratification pattern. The pattern of each contour displacement segment is determined as follows: the temperature at the geometric center of the high-temperature core minus 3 degrees Celsius is used as the high-temperature threshold for that frame. The connected pixel regions in the neighborhood of the geometric center of the high-temperature core in two adjacent frames whose temperature exceeds the high-temperature threshold are taken as the high-temperature contour projection area on that frame. The ratio of the intersection area to the union area of ​​the high-temperature contour projection areas of the two frames is calculated as the region overlap rate. If the region overlap rate is greater than the preset overlap threshold of 0.7, and the vertical position difference of the geometric center of the high-temperature core in the two frames is less than the preset dwell displacement threshold of 0.03 meters, then the displacement segment is determined to be a continuous overlapping segment attached to the box wall. The preset dwell displacement threshold is determined according to the statistical upper bound of the vertical swing amplitude of the adjacent frames of the attached segment. The continuous overlapping sections attached to the tank wall are characterized by the high-temperature core briefly staying on the same section of the tank wall, maintaining a generally consistent geometric shape. Another type of discrimination is based on vertical cross-layering: the oil temperature stratification pattern is refined based on the linear interpolation obtained from the top and bottom platinum resistance temperature measurement points in S103. Temperature measurement points are added at equal intervals of 0.05 meters along the vertical direction of the oil tank. The average temperature of each temperature measurement point within 5 consecutive minutes after the operation enters the thermal steady state is taken. The temperature measurement points are arranged from low to high vertically and fitted with cubic splines along the vertical direction to form a continuous temperature distribution curve, which serves as the basic data for querying the stratified oil temperature reference value. Then, from the oil temperature stratification pattern, according to the monotonically increasing temperature from bottom to top, the adjacent vertical height range corresponding to the temperature increase reaching the preset increase threshold of 1 degree Celsius is divided into a vertical layer, resulting in several vertical layers numbered sequentially from low to high vertically. If the starting point of a certain contour displacement segment falls within a lower-numbered vertical layer and its ending point falls within an adjacent higher-numbered vertical layer, and the vertical displacement from the starting point to the ending point is greater than a preset upward displacement threshold of 0.1 meters, then the displacement segment is determined to be an upward displacement segment across the oil layer.

[0055] Preferably, the vertical expansion boundary follows the vertical expansion boundary determined by the outer edge curve determined by the lateral temperature gradient decay. When the high-temperature core approaches the top of the tank and the outer edge curve is difficult to extend further, the first of the following two conditions is taken as the upper end of the vertical expansion boundary: First, the vertical coordinate on the tank wall development surface reaches the layer where the top overflow port is located; second, the upward movement rate of three consecutive sampling points in the vertical direction is less than 0.02 meters per second, which is considered as the termination of the upward trend of thermal energy. The continuous overlapping segments attached to the tank wall are connected separately in time sequence to obtain the attached segment chain, and the upward movement segments across the oil layer are connected separately in time sequence to obtain the upward movement segment chain. The two chains correspond one-to-one on the time axis and are arranged alternately. On the time axis of the two chains, at each moment of transition from the attached segment to the adjacent upward movement segment, the lateral and vertical coordinates of the sampling point before and after that moment on the tank wall development surface are taken as the arithmetic mean to obtain the two-dimensional coordinates at that moment, which are marked as the junction position. Starting from the initial layer, and proceeding in ascending order of time, the first cross-layer upward segment of the upward segment chain is connected. Then, at its end, it connects with the corresponding continuous overlapping segment of the attached box wall in the attached segment chain. From the intersection of this attached segment, the next cross-layer upward segment in the upward segment chain is led out. This connection is repeated in the corresponding order of the two chains until the vertical expansion boundary is reached, thus forming the plume channel for fault thermal energy. The plume channel is characterized by the attached segment chain depicting the path of thermal energy's lateral retention and displacement along the box wall, and the upward segment chain depicting the path of thermal energy's upward transport from the interior along the oil flow. After being connected at the intersection, the two chains completely present the direction of fault thermal energy being temporarily intercepted by the box wall before continuing to rise.

[0056] Step S105: Use a hot oil plume transport model to analyze the plume channel and vertical expansion boundary, trace the rising path of hot oil along the initial emergence layer, and identify the internal search area defined by the axial section and the direction of the adjacent box wall.

[0057] The plume channel and the vertical expansion boundary are obtained. A hot oil plume transport model is used to fit the horizontal displacement distribution with height at each intersection position on the plume channel and its adjacent cross-oil layer upward movement segment under buoyancy drive, resulting in a plume rising path reflecting the displacement displacement distribution with height during the upward transport of hot oil from the initial appearance layer. The hot oil plume transport model adopts an axisymmetric turbulent buoyancy plume model, using the coordinates of the intersection position and the vertical displacement of the cross-oil layer upward movement segment as fitting inputs, and the horizontal displacement relative to the tank wall at the corresponding height as fitting output. The plume rising path is traced along the initial appearance layer, and the horizontal displacement of the plume rising path at the initial appearance layer is mapped in the opposite direction to the internal space of the tank, obtaining a candidate axis extending inward from the tank wall. The horizontal distance between the candidate axis and the transformer winding column is obtained, and the axial segment of the winding column corresponding to the candidate axis is determined. The portion of the winding column height within the height limit of the vertical expansion boundary is labeled as the axial segment. Obtain the side of the box wall to which the axial section is attached and the plume channel is attached. Take the normal direction of the inner surface of the side of the box wall as the direction of the adjacent box wall. Extend the direction of the adjacent box wall from the inner surface of the box wall inward to the vertical plane where the candidate axis is located. Take the three-dimensional space enclosed by the vertical direction of the axial section and the horizontal direction of the adjacent box wall as the internal search area.

[0058] When an internal overheating fault occurs in an oil-immersed transformer, the heat released at the fault point first heats the adjacent oil layer. The increased oil temperature leads to a decrease in density, and driven by buoyancy, the hot oil moves vertically upward, entraining cooler surrounding oil along the way, forming a hot oil plume that extends upward from the fault point. As the hot oil plume rises, it deviates from directly above the fault point, eventually carrying the fault's thermal energy to higher areas of the transformer wall. This is the physical source of the shift in the location of the high-temperature core observed outside the transformer wall.

[0059] Specifically, the hot oil plume transport model adopts an axisymmetric turbulent buoyancy plume model. This model considers the hot oil plume as a steady-state plume formed by the continuous release of buoyancy flux from a single buoyancy source within an infinitely large, uniform background oil. The model posits that during its upward movement, the plume's radius expands linearly with height, while the upward velocity of its centerline decreases exponentially with height. Simultaneously, due to entrainment, the plume absorbs surrounding oil in a certain proportion along the horizontal direction. When a horizontal temperature gradient or weak disturbances in the background oil flow are present, the plume's centerline will shift horizontally during its ascent, with the shift monotonically increasing with increasing height from the source.

[0060] In one possible implementation, the spatial coordinates of each intersection position on the plume channel and the vertical displacement of the adjacent upward segment across the oil layer are used as fitting samples and substituted into the axisymmetric turbulent buoyancy plume model. The plume radius expansion rate and the entrainment coefficient in the model are taken as undetermined parameters. The plume radius expansion rate determines the linear slope of the plume radius with height, and the entrainment coefficient determines the power law coefficient of the horizontal offset of the centerline with height. Substituting both into the model yields the predicted value of the horizontal offset at any height. Using the least squares method, the plume radius expansion rate, the entrainment coefficient, and the lateral reference coordinate x0 of the position directly above the plume source on the developed surface of the box wall are taken as common undetermined parameters. The lateral coordinate of the plume centerline at any height predicted by the model is the sum of x0 and the predicted value of the horizontal offset at that height. The observable lateral coordinates of each of the intersection positions and the adjacent sampling points of the cross-oil layer upward movement segment on the developed surface of the box wall are used as the fitting target to minimize the sum of squares of the differences between the predicted lateral coordinates and the actual lateral coordinates. This yields the plume ascent path, which reflects the distribution of displacement offset with height during the upward movement of hot oil from its initial layer. The plume ascent path consists of a series of height values ​​and their corresponding horizontal offsets relative to the box wall.

[0061] It should be noted that the height at which the fault source is first detected on the tank wall is the initial occurrence layer. The horizontal offset given by the plume rising path at this height represents the distance that the hot oil has drifted horizontally relative to directly above the fault source when it rises from the internal fault source to this height.

[0062] Specifically, the horizontal offset δ0 of the plume's rising path at the initial emergence level is extracted; the lateral coordinates of the wall observation point at the initial emergence level are moved back by δ0 in the opposite direction of the drift to obtain the lateral coordinates directly above the plume source. This position is then shifted inward along the normal direction of the tank wall by the absolute value of δ0 to obtain a reverse mapping point extending inward from the tank wall. The normal shift is set to be equal to the horizontal offset in this embodiment. Using this reverse mapping point as the starting point, an upward extension is made along the direction parallel to the transformer core axis to the upper limit of the vertical extension boundary, and simultaneously downward to 0.05 meters below the initial emergence level, forming a candidate axis located inside the tank. This candidate axis represents the vertical spatial line connecting the possible locations of the fault source after stripping away the oil flow transport drift component.

[0063] Preferably, when there are multiple plume upflow paths, the above-mentioned reverse mapping is performed on each plume upflow path to obtain multiple reverse mapping points; the coordinates of the multiple reverse mapping points are averaged along the horizontal direction to obtain a summing starting point, and a candidate axis is regenerated according to the above-mentioned extension rules based on the summing starting point for subsequent alignment.

[0064] In one embodiment, the horizontal positions of each winding column axis are pre-obtained inside the enclosure according to the transformer structure diagram. The horizontal coordinates of the candidate axis are sequentially subtracted from the horizontal coordinates of each winding column axis, and the winding column with a horizontal spacing less than a preset alignment threshold of 0.1 meters is selected as the winding column corresponding to the candidate axis. If no winding column meets the condition, the winding column with the smallest horizontal spacing is selected as the winding column corresponding to the candidate axis. Further, the height segment occupied vertically from the top end face to the bottom end face of the winding column corresponding to the candidate axis is taken as the winding section height of that winding column. The intersection of the winding section height and the height range limited by the vertical extension boundary is calculated, and the height segment occupied by the intersection is marked as the axial section. The axial section represents the possible location of the fault source along the winding column height direction. The side of the enclosure wall to which the axial section is attached is obtained, and the normal direction pointing from the inner surface of the side of the enclosure wall towards the inside of the enclosure is marked as the adjacent enclosure wall direction. The direction of the adjacent box wall is horizontal, pointing from the attached side box wall to the vertical plane where the candidate axis is located.

[0065] Specifically, taking the inner surface of the attached sidewall as the starting point, the horizontal extension segment extends inward along the direction of the adjacent sidewall to the vertical plane where the candidate axis is located, thus obtaining a horizontal extension segment along the direction of the adjacent sidewall. The three-dimensional space enclosed by the horizontal extension segment and the vertical height segment limited by the axial section is defined as the internal search area. The internal search area is defined vertically by the axial section and horizontally by the direction of the adjacent sidewall, thus eliminating the vertical and horizontal transport offset components of the oil flow, providing a convergent spatial limit for the subsequent extraction of the thermal energy accumulation boundary along the plume channel inside the box.

[0066] Step S106: Obtain the local oil temperature within the internal search area, identify the internal oil layer and reflux interface that the hot oil passes through when it travels from the heat source to the tank wall, extract the heat energy accumulation boundary along the plume channel, and form a candidate area for the fault source.

[0067] The local oil temperature collected by the distributed optical fiber temperature measurement points deployed in the internal search area is obtained. The local oil temperature is arranged into a two-dimensional oil temperature field along the vertical direction and along the adjacent tank wall direction according to its spatial coordinates. The continuous segment in the two-dimensional oil temperature field where the local oil temperature increases monotonically from bottom to top vertically and the temperature difference between adjacent measurement points is greater than a preset increment threshold of 0.5 degrees Celsius is identified. The continuous segment is marked as the internal oil layer that the hot oil passes through when it travels from the heat source to the tank wall. In the two-dimensional oil temperature field, the bottom oil temperature is obtained as a background reference. A transition zone is identified where the local oil temperature drops sharply from top to bottom vertically, with a difference of less than 1 degree Celsius from the bottom oil temperature. This transition zone is marked as the reflux interface where the cooled oil returns to the bottom of the tank. A vertical cross-section is taken along the direction of the plume channel, extending from the bottom of the plume channel upwards to the top of the plume channel and penetrating the internal oil layer and the reflux interface. The intermediate oil temperature readings at the top of the internal oil layer and the bottom of the reflux interface on the cross-section, and the intermediate oil temperature readings between them, are linearly interpolated according to the measurement point spacing and taken as the arithmetic mean, which is used as the boundary oil temperature. The set of connected pixels in the two-dimensional oil temperature field where the local oil temperature is higher than the boundary oil temperature is marked, thus obtaining the heat energy accumulation boundary. Within the internal search area, the space occupied by the set of connected pixels enclosed by the heat energy accumulation boundary is taken, and the portion of the space within the range defined by the axial section and the adjacent tank wall direction is marked as the candidate fault source area.

[0068] When an internal overheating fault occurs in an oil-immersed transformer, hot oil flows from the fault source, rises to the tank wall, cools, and then slowly sinks back down along the sides and bottom of the tank to the bottom of the windings, forming a relatively stable natural convection loop inside the tank. The internal search area is located within a section of this convection loop, containing both a high-temperature oil layer rising along the plume channel and a low-temperature return flow descending along the tank wall. Identifying the spatial boundary between these two layers is the physical basis for extracting the boundary of heat energy accumulation.

[0069] Specifically, a distributed optical fiber temperature measurement network is pre-laid inside the transformer tank along the gaps between each winding post and the four side tank walls: after the optical fiber enters the gap from the bottom of the tank, it is laid in a serpentine pattern along the tank wall direction between the winding post and the tank wall in each vertical laying layer, covering the horizontal width of the gap along the tank wall direction. Then, the laying layer is moved vertically upwards and the reverse serpentine pattern is repeated. This process is repeated layer by layer upwards to the top of the winding post, so that the temperature measurement points are distributed in a grid pattern along the tank wall direction and adjacent tank wall direction in both the vertical and horizontal planes. In this step, according to the adjacent tank wall direction and the internal search area determined in S105, the temperature measurement point readings that fall into the internal search area in the corresponding side gap are retrieved.

[0070] For example, the vertical spacing between measuring points is 0.05 meters to 0.1 meters, and the horizontal spacing between measuring points is 0.05 meters. Within the internal search area, local oil temperatures are collected from the distributed optical fiber temperature measuring points to obtain a local oil temperature dataset covering the internal search area.

[0071] In one possible implementation, the readings of each measuring point in the local oil temperature dataset are arranged according to their spatial coordinates, with the vertical height as the ordinate and the horizontal distance along the adjacent tank wall as the abscissa, forming a two-dimensional oil temperature field along the vertical and adjacent tank wall directions. The two-dimensional oil temperature field is presented in pixel form, with each pixel storing the local oil temperature value at that spatial location.

[0072] It should be noted that in the transport channel from the heat source to the tank wall, the oil temperature increases monotonically from bottom to top vertically, and the temperature difference between adjacent heights is much greater than the temperature change in the reflux section after cooling at the same height.

[0073] In one embodiment, the two-dimensional oil temperature field is scanned vertically column by column to identify continuous measuring point segments that monotonically increase vertically from bottom to top and whose temperature difference between adjacent measuring points is greater than a preset increment threshold of 0.5 degrees Celsius. The spatial region composed of these continuous measuring point segments is then labeled as the internal oil layer that the hot oil passes through as it travels from the heat source to the tank wall. The internal oil layer reflects the main path of the hot oil as it is transported upwards along the plume channel.

[0074] Specifically, the reflux section where the cooled oil returns to the bottom of the tank is adjacent to the internal oil layer but in the opposite direction, and its temperature decreases with height to near the bottom oil temperature. A vertical scan is performed from top to bottom in the two-dimensional oil temperature field, and the temperature difference between two adjacent measuring points is taken as the vertical temperature drop at that point. A continuous measuring point band is identified where the vertical temperature drop exceeds a preset drop threshold of 2 degrees Celsius, and the difference between the local oil temperature and the bottom oil temperature after this drop is less than 1 degree Celsius. The spatial area occupied by this continuous measuring point band is marked as the reflux interface where the cooled oil returns to the bottom of the tank. The reflux interface and the internal oil layer are spatially located on opposite sides of the plume channel.

[0075] Preferably, along the direction of the plume channel, a vertical cross-section extending from the bottom to the top of the plume channel is taken from the inner oil layer to the reflux interface. Local oil temperatures at the top of the inner oil layer and at the bottom of the reflux interface are measured along this cross-section. When the two measuring points are not directly adjacent vertically, several intermediate oil temperature readings are first obtained by linear interpolation along the cross-section between them according to the distance between the measuring points. Then, the arithmetic mean of the oil temperature readings at the top of the inner oil layer, the bottom of the reflux interface, and the several intermediate oil temperature readings is calculated to obtain the boundary oil temperature. Pixels in the two-dimensional oil temperature field with local oil temperatures higher than the boundary oil temperature are connected into a set, resulting in a set of connected pixels located within the inner oil layer where local oil temperatures are relatively concentrated. The outer contour of this set of connected pixels is the thermal energy accumulation boundary. This thermal energy accumulation boundary spatially delineates the core area where the hot oil's thermal energy is relatively concentrated before reaching the tank wall. Within the internal search area, the thermal energy accumulation boundary is stretched along the direction perpendicular to the two-dimensional oil temperature field, i.e., along the tank wall, according to the width of the internal search area along the tank wall, to obtain a three-dimensional space enclosed by the thermal energy accumulation boundary; the portion of the three-dimensional space within the vertical height range limited by the axial section and within the horizontal extension range limited by the adjacent tank wall direction is marked as a candidate fault source area.

[0076] Understandably, the candidate fault source region further narrows the space within the internal search area that carries the heat source, providing a directly searchable physical range for subsequent identification of the heat source along the hot oil passage.

[0077] Step S107: Identify the heat source along the hot oil passage within the candidate fault source area, analyze the coverage direction of the accumulation boundary on the multi-sided tank wall, assess the fault range extending along the adjacent tank wall within the axial section, lock the internal overheating fault area, and complete the fault detection and location of the oil-immersed transformer.

[0078] Obtain distributed oil temperature measurement point readings within the candidate fault source area. Connect the continuous measurement points along the plume channel, where the local oil temperature monotonically increases vertically from bottom to top, to form a main heating path. Trace back from the lower starting point of the main heating path to the lowest continuous high-temperature measurement point string within the candidate fault source area. Mark the spatial channel traversed by this lowest continuous high-temperature measurement point string as the hot oil passage channel. Take the local oil temperature weighted geometric center of the high-temperature pixel set connected at the bottom of the hot oil passage channel as the heat source, thus obtaining the location of the heat source within the candidate fault source area. Obtain the projection distribution of the heat energy accumulation boundary on the multi-sided tank wall. Take the boundary segment where the shortest vertical distance between the heat energy accumulation boundary and the inner surface of each side tank wall is less than a preset wall-attachment distance threshold of 0.05 meters. Mark the side of the tank wall to which the boundary segment is attached as the coverage side. Take the normal of the inner surface of the coverage side as the coverage direction of the boundary segment. This yields the coverage direction of the heat energy accumulation boundary on the multi-sided tank wall. Starting from the location of the heat source, along the horizontal direction indicated by each of the coverage directions, extend horizontally towards the adjacent tank wall corresponding to the covered side within the vertical height range limited by the axial section to obtain the extension path; take the horizontal span occupied by the set of connected pixels on the extension path whose local oil temperature is higher than the boundary oil temperature as the fault range extending along the adjacent tank wall direction; lock the three-dimensional space enclosed by the fault range and the axial section as the internal overheat fault area, and complete the fault detection and location of the oil-immersed transformer.

[0079] When an internal overheating fault occurs in an oil-immersed transformer, the fault source continuously releases heat and heats the adjacent oil. The heated oil is transported upwards along the winding gaps and oil passages in the form of hot oil. The candidate fault source region has narrowed the space for the heat source to a finite volume, but the precise location of the heat source within this volume still needs to be traced backwards by the direction of the hot oil flowing from the inside out.

[0080] Specifically, starting from the distributed oil temperature measurement points within the candidate fault source area, adjacent measurement points whose local oil temperature monotonically increases vertically from bottom to top are connected in series until the heating trend is interrupted or exceeds the upper boundary of the candidate fault source area, thus obtaining a main heating path. The main heating path is connected solely based on the monotonous increase in temperature from bottom to top, reflecting the main upward flow direction of hot oil within the candidate fault source area.

[0081] In one possible implementation, the process continues tracing along the lower starting point of the main heating path into the candidate fault source region. Continuous measuring points located below the vertical height of the lower starting point of the main heating path, where the local oil temperature is higher than the boundary oil temperature, are connected in series downwards until the local oil temperature of each continuous measuring point is lower than the boundary oil temperature. This results in a lowermost continuous string of high-temperature measuring points located below the main heating path. The spatial channel traversed by this lowermost continuous string of high-temperature measuring points is designated as the hot oil passage channel. This hot oil passage channel, with its upper end connecting to the main heating path and its lower end pointing towards the location of the heat source, represents a transitional path of hot oil before it overflows from the heat source and enters the main heating path along the oil channel. Furthermore, the set of adjacent high-temperature pixels connected to the lower end of the hot oil passage is taken. For each pixel in this set, the difference between its local oil temperature and the boundary oil temperature is used as a weight. This weight is multiplied dimension by dimension by the spatial coordinates of the pixel and then summed. The result is divided by the sum of all weights to obtain the coordinates of the weighted geometric center of the local oil temperature. This coordinate is then marked as the location of the heat source. The location of the heat source corresponds to the physical location of the fault source within the fault source candidate region.

[0082] It should be noted that the thermal energy accumulation boundary is the outer contour of the set of connected pixels in the two-dimensional oil temperature field where the local oil temperature is higher than the boundary oil temperature. In space, it appears as a closed curve surrounding the high-temperature core region. Projecting this closed curve onto the vertical plane containing the inner surface of each side wall of the transformer yields the projection distribution of the thermal energy accumulation boundary on the multiple side walls.

[0083] In one embodiment, the shortest vertical distance from each boundary segment on the thermal energy accumulation boundary to the inner surface of each side box wall is calculated sequentially. This shortest vertical distance is measured along the normal direction of the box wall, from a sampling point on the boundary segment along a direction perpendicular to that side box wall to the inner surface of the box wall. If the shortest vertical distance from a boundary segment to a side box wall is less than a preset wall-attachment distance threshold of 0.05 meters, then the boundary segment is determined to be attached to that side box wall; this side box wall is marked as the covering side, and the normal direction pointing from the inner surface of the covering side into the box body is taken as the covering direction of the boundary segment. If the same boundary segment simultaneously satisfies the wall-attachment conditions of multiple side box walls, then the boundary segment is sequentially assigned to the covering side corresponding to each satisfying box wall, and each is assigned a corresponding covering direction, allowing a boundary segment to have multiple covering directions.

[0084] Preferably, the heat energy accumulation boundary is arranged according to the orientation of the box wall according to the multiple coverage directions obtained by the above determination, forming a convergence of coverage directions of the heat energy accumulation boundary on multiple box walls. The convergence of coverage directions describes the box wall orientation combination that the fault heat energy preferentially points to when it diffuses from the inside to the outside, reflecting the heat dissipation advantage of the heat source. The axial section adopts the height segment obtained by intersecting the height of the winding column section and the height range limited by the vertical extension boundary in S105 as a fixed definition for vertical enclosure. When there are multiple unconnected high-temperature measuring point strings on the extension path, the measuring point string that is horizontally continuous and uninterrupted from the position of the heat source is preferentially selected, and the horizontal distance from the farthest end of the string to the heat source is taken as the horizontal span in the coverage direction; if each segment is not continuous and reachable, the measuring point string closest to the corresponding box wall is selected, and its farthest end position is marked for verification. The horizontal span of each coverage direction is marked on the horizontal plane according to the box wall orientation, and together with the axial section, they enclose the internal overheating fault area.

[0085] It is understandable that the internal overheating fault area defines the spatial boundaries of the fault source in both the vertical segment and the horizontal orientation of the area inside the tank. This layer-by-layer peels away the apparent shift caused by the upward movement and horizontal spread of the high-temperature area on the tank wall surface due to the increased heat generation power of the fault, thus completing the fault detection and location of the oil-immersed transformer.

[0086] The thermal energy accumulation boundary of the hot oil passage in the candidate fault source area at the initial occurrence layer is extracted, the intersection of each passage from the internal oil layer to the adjacent box wall is marked, and the intersection of the same axial section is connected in series according to the coverage direction on multiple box walls to delineate the fault range extending along the box wall direction.

[0087] The hot oil passages within the candidate fault source area are obtained. A horizontal cross-section is taken at the vertical height of the initial occurrence layer along the direction of each hot oil passage. The closed contour enclosed by the thermal energy accumulation boundary on this horizontal cross-section is taken as the horizontal cross-sectional thermal energy boundary of the passage at the initial occurrence layer. On the horizontal cross-sectional thermal energy boundary, an arc segment where the inner surface of the internal oil layer and the inner surface of the corresponding adjacent tank wall contact and overlap is taken as the contact arc segment. The equidistant midpoints along the contact arc segment are marked as the intersection points where the hot oil passage enters the adjacent tank wall from the internal oil layer, thus obtaining the intersection points corresponding to each hot oil passage. According to the coverage direction of the heat energy accumulation boundary on the multi-sided box wall, the intersection positions falling in the same axial section are connected in series with the heat source position as the pole and the azimuth angle of each intersection position relative to the pole from small to large, to obtain a line segment connected in sequence along the box wall direction. The horizontal segment through which the line segment passes is defined as the fault range extending along the box wall direction.

[0088] Within the hot oil passage, hot oil is transported upwards from the source of the fault along the oil channel. Along the way, it first passes through the internal oil layer, then crosses the interface between the internal oil layer and the tank wall to reach the adjacent tank wall. This interface is the entry point for hot oil from the internal oil layer into the adjacent tank wall. It is arc-shaped on the horizontal cross-section where the initial layer appears. Determining the coordinates of the entry point on this arc yields the intersection point of the hot oil passage, constituting a key node for locating the fault range along the tank wall direction.

[0089] Specifically, each of the hot oil passage channels is extracted from the candidate fault source area. Each hot oil passage channel is arranged in its spatial direction from bottom to top and extends to the vertical height of the initial occurrence layer. A horizontal cross-section is made at this vertical height to obtain the horizontal cross-section of the hot oil passage channel at the initial occurrence layer.

[0090] In one possible implementation, the readings of all measuring points within the distance between one measuring point above and one below the horizontal cross-sectional height layer of the distributed optical fiber temperature measuring points are taken, and spread out onto the horizontal cross-section according to their spatial coordinates on the horizontal plane to obtain local oil temperature pixels distributed on the horizontal cross-section; adjacent pixels with local oil temperatures higher than the boundary oil temperature are connected into a set, and the outer contour of the connected pixel set is taken as the horizontal cross-sectional thermal energy boundary of the hot oil passage at the initial appearance layer.

[0091] In one embodiment, the horizontal cross-sectional thermal boundary is a closed curve surrounding the hot oil passage. A portion of the arc adheres closely to the inner wall of the transformer tank along the direction of the adjacent inner surface of the tank wall, while another portion curves inwards towards the tank. Using the same adhesion measurement employed in the step of determining the boundary segment's adhesion to the tank wall, a continuous arc on the horizontal cross-sectional thermal boundary with a distance along the tank wall normal less than a preset adhesion distance threshold of 0.05 meters is taken as the contact arc segment where the internal oil layer and the inner surface of the adjacent tank wall are in contact and overlap.

[0092] Specifically, the sampling points along the contact arc segment are accumulated point by point according to the arc length, starting from one end. The sampling point corresponding to the point where the accumulated value reaches half the total length of the contact arc segment is taken as the equidistant midpoint of the contact arc segment. In one embodiment, the horizontal coordinates of the equidistant midpoints are marked as the intersection point where the hot oil passage enters the adjacent tank wall from the internal oil layer. The intersection point is the inlet coordinate of the hot oil passage touching the adjacent tank wall at the initial layer appearance position.

[0093] It should be noted that there are often multiple hot oil passages within the same axial section, and their corresponding multiple intersection points will be attached to the box wall on different sides, reflecting the multiple inlet points radiated by the heat source along the box wall direction.

[0094] Preferably, the intersection locations are grouped according to the sides of the box wall to which they are attached. Within the same axial segment, the projection point of the heat source location on the horizontal plane where the initial layer appears is taken as the pole. Rays are drawn from the pole to each intersection location, and the angle formed by the ray relative to a certain fixed horizontal reference direction is taken as the azimuth angle of the intersection location relative to the pole.

[0095] For example, the projection direction of the longitudinal centerline of the transformer onto the horizontal plane is taken as a fixed horizontal reference direction, and the azimuth angle is measured from 0 degrees to 360 degrees in the counterclockwise direction.

[0096] Furthermore, the intersection positions within the same axial segment are arranged in ascending order of their azimuth angles. Adjacent intersection positions are then connected end-to-end according to the orientation of the heat energy accumulation boundary on the multi-sided box wall, resulting in line segments connected sequentially along the box wall direction. These line segments are arranged around the pole in azimuth order, passing through the box wall segments on each covered side.

[0097] In one embodiment, the horizontal segment that the connecting line segment traverses from its starting point to its ending point along each covered side wall is defined as the fault range extending along the wall direction. This fault range, presented as a horizontally oriented region, specifically describes the distribution of fault-induced heat along the wall direction on the horizontal plane where the initial occurrence layer is located.

[0098] The above description is merely a specific implementation of this specification. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the scope of protection of this specification is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this specification, and these modifications or substitutions should all be covered within the scope of protection of this specification.

Claims

1. A method for fault detection and location in an oil-immersed transformer, characterized in that, The method includes: Continuous infrared video of multiple outer surfaces of the fuel tank is acquired, and the continuous images are organized according to the coverage of each side of the tank wall. The continuous outline of the heating area in the front and back images is identified to form a dynamic temperature distribution that reflects the heating process of the tank wall. Identify high-temperature regions in dynamic temperature distribution, exclude uniformly heated regions formed by the top oil temperature background, extract the upward trajectory of the high-temperature core formed by the extension of the initial layer, and delineate the vertical expansion boundary. Acquire the load history and cooling conditions during operation, read the top oil temperature and bottom oil temperature, analyze the heat energy distribution of the upper and lower oil layers, and identify the oil temperature stratification morphology formed by natural oil circulation. Analyze the upward trajectory of the high-temperature core and the oil temperature stratification morphology, identify the heating profile that stays in the local area of ​​the tank wall and the extended profile that rises with the oil layer, distinguish between local heating in the tank wall and heating carried by the oil flow, and form a plume channel for fault thermal energy. A hot oil plume transport model was used to analyze the plume channel and vertical expansion boundary, and the hot oil rising path was traced along the initial emergence layer to identify the internal search area defined by the axial section and the direction of the adjacent box wall. The local oil temperature within the internal search area is obtained, the internal oil layer and reflux interface that the hot oil passes through when it flows from the heat source to the tank wall are identified, and the heat energy accumulation boundary is extracted along the plume channel to form a candidate area for the fault source. Identify the heat source by traversing the hot oil passage within the candidate fault source area, analyze the coverage direction of the accumulation boundary on multiple side walls, assess the fault range extending along the adjacent wall within the axial section, and pinpoint the internal overheating fault area.

2. The method for fault detection and location of an oil-immersed transformer according to claim 1, characterized in that, The process of acquiring continuous infrared video of the outer surfaces of multiple sides of the fuel tank, organizing the continuous images according to the coverage area of ​​each side of the tank wall, identifying the continuous outline of the heating area in the preceding and following images, and forming a dynamic temperature distribution reflecting the heating process of the tank wall includes: Infrared cameras are deployed on the outside of the four side walls to acquire continuous infrared video. The continuous images are spliced ​​and time-aligned according to the coverage of each side wall to obtain a sequence of infrared images for each side. Inter-frame contour matching is used to track the position of the heating zone in adjacent images. The boundary of the same heating zone is connected to obtain a continuous contour and superimposed along the time axis to obtain a dynamic temperature distribution.

3. The method for fault detection and location of an oil-immersed transformer according to claim 1, characterized in that, The process of identifying high-temperature regions in dynamic temperature distribution, excluding uniformly heated regions formed by the top oil temperature background, extracting the upward trajectory of the high-temperature core formed by the extension of the initial layer, and delineating the vertical expansion boundary includes: The connected regions whose temperatures exceed a preset temperature threshold are extracted from the dynamic temperature distribution as high-temperature zones. The top oil temperature background with a horizontal temperature difference less than a preset amplitude at the top of the tank wall is removed. The vertical height of the earliest appearing connected region with an outline area exceeding a preset minimum area is taken as the initial appearance layer. The centroid of the candidate high-temperature zones is obtained by tracking the centroids frame by frame to obtain the upward trajectory of the high-temperature core. The position of the tank wall where the horizontal temperature gradient decays to a preset gradient threshold is taken as the outer edge of the vertical expansion boundary.

4. The method for fault detection and location of an oil-immersed transformer according to claim 1, characterized in that, The process of reading the top and bottom oil temperatures, analyzing the thermal energy distribution of the upper and lower oil layers, and identifying the oil temperature stratification morphology formed by natural oil circulation includes: The top oil temperature is read from the temperature measuring point at the top of the chamber, and the bottom oil temperature is read from the temperature measuring point at the bottom of the chamber. The oil temperature distribution is obtained by linear interpolation along the height of the chamber according to the thermal buoyancy stratification law, with the top oil temperature and the bottom oil temperature as the two vertical endpoints. The oil temperature distribution with the calibrated temperature increasing monotonically from bottom to top and the temperature difference between the top and bottom being within the preset temperature difference range is the oil temperature stratification form.

5. The method for fault detection and location of an oil-immersed transformer according to claim 1, characterized in that, The analysis of the high-temperature core's upward trajectory and oil temperature stratification morphology identifies the heating profile localized on the tank wall and the extended profile that rises with the oil layer, distinguishing between localized heating on the tank wall and heating carried by the oil flow, forming a plume channel for fault thermal energy, including: The vertical height of each sampling point on the high-temperature core rising trajectory is substituted into the oil temperature stratification pattern. The oil temperature at the same vertical height is taken as the stratification oil temperature reference value. The abnormal trajectory segment sequence with the sampling point temperature exceeding the stratification oil temperature reference value is calibrated. The displacement segments between adjacent sampling points of the abnormal trajectory segment sequence are classified, and the displacement segments attached to the inner surface of the tank wall are determined to be heating profiles that remain in the local area of ​​the tank wall, and the displacement segments that extend upward along the high oil temperature layer are extended profiles that float with the oil layer. The heating profile that remains on the local wall of the tank and the extended profile that rises with the oil layer are connected in series and the intersection of the two are marked. The plume channel of the fault thermal energy is obtained by collecting the intersections.

6. The method for fault detection and location of an oil-immersed transformer according to claim 5, characterized in that, The identification of localized heating profiles on the tank wall and extended profiles rising with the oil layer, distinguishing between localized heating on the tank wall and heating carried by the oil flow, forms a plume channel for fault thermal energy, including: The vertical height of the sampling point where the first abnormal temperature rise occurs on the high-temperature core's upward trajectory is taken as the initial occurrence layer. The contour displacement segment between the initial occurrence layer and the vertical expansion boundary is intercepted along the high-temperature core's upward trajectory. This segment is then included in the continuous overlapping segments attached to the box wall at the same vertical height and with a regional overlap rate exceeding a preset overlap threshold. This segment is also included in the upward migration segment across adjacent vertical layers. The continuous overlapping segments attached to the box wall and the upward migration segment across the oil layer are connected in series, and the intersection position is marked to obtain the plume channel.

7. The method for fault detection and location of an oil-immersed transformer according to claim 1, characterized in that, The method of using a hot oil plume transport model to analyze the plume channel and vertical expansion boundary, and tracing the upward path of hot oil along the initial emergence layer, includes: The hot oil plume transport model adopts an axisymmetric turbulent buoyancy plume model. The plume rise path is obtained by using the intersection position coordinates and the vertical displacement of the upward segment across the oil layer as the fitting input and the horizontal offset of the corresponding height relative to the box wall as the fitting output. The plume rise path is tracked along the initial appearance layer and mapped into the box to obtain candidate axes. The part of the winding column corresponding to the candidate axis within the height limited by the vertical extension boundary is calibrated as the axial segment. The three-dimensional space enclosed by the axial segment along the vertical direction and the adjacent box wall along the horizontal direction is taken as the internal search area.

8. The method for fault detection and location of an oil-immersed transformer according to claim 1, characterized in that, The acquisition of the local oil temperature within the internal search area includes: The local oil temperatures are arranged into a two-dimensional oil temperature field according to spatial coordinates. The continuous section with a monotonically increasing vertical temperature and a temperature difference between adjacent measuring points greater than a preset increasing threshold is defined as the internal oil layer. The transition zone where the oil temperature suddenly drops to a level less than a preset threshold and the difference between the oil temperature and the bottom layer oil temperature is defined as the reflux interface. The arithmetic mean of the oil temperatures at the top of the internal oil layer and the bottom of the reflux interface is taken as the boundary oil temperature. The set of connected pixels with local oil temperatures higher than the boundary oil temperature is defined as the thermal energy accumulation boundary to obtain the candidate fault source region.

9. The method for fault detection and location of an oil-immersed transformer according to claim 1, characterized in that, The process of identifying heat sources along the hot oil flow path within the candidate fault source region and analyzing the coverage direction of the accumulation boundary on multiple tank walls includes: The main heating path is formed by connecting continuous measuring points with monotonically increasing local oil temperature along the plume channel. The continuous high-temperature measuring point string from the bottom of the main heating path to the bottom is calibrated as the hot oil passage channel. The weighted geometric center of the high-temperature pixel set at the bottom of the hot oil passage channel is taken as the heat source. The side of the box wall to which the shortest vertical distance between the calibrated heat energy accumulation boundary and the inner surface of the box wall is less than the preset wall-attaching distance threshold is the covering side, and the normal of the inner surface of the covering side is taken as the covering direction. Extending horizontally along each coverage direction from the heat source within the vertical height limited by the axial section, the horizontal span of the set of connected pixels where the local oil temperature is higher than the boundary oil temperature is taken as the fault range, and the three-dimensional space enclosed by the fault range and the axial section is defined as the internal overheating fault area.

10. The method for fault detection and location of an oil-immersed transformer according to claim 9, characterized in that, The continuous high-temperature measuring point string traced from the lower end of the main heating path to the lowest end is calibrated as a hot oil passage channel, and the weighted geometric center of the high-temperature pixel set at the bottom of the hot oil passage channel is taken as the heat source, including: Take a horizontal cross-section at the initial layer height of each hot oil passage, and take the closed contour enclosed by the heat energy accumulation boundary as the horizontal cross-section heat energy boundary. Take the arc line that coincides with the contact of the inner oil layer and the inner surface of the adjacent tank wall as the contact arc segment. Mark the equidistant midpoints of the contact arc segment as the intersection of the hot oil passage from the inner oil layer to the adjacent tank wall. Connect the intersections in the same axial section according to the coverage direction to obtain the fault range extending along the tank wall direction.

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